Field
This disclosure relates to multiphase flow measurement devices and more particularly to multiphase-flow water conductivity probes that may be used standalone or with multiphase flow meters.
Description of the Related Art
Wells are generally drilled into subsurface rocks to access fluids, such as hydrocarbons, stored in subterranean formations. The subterranean fluids can be produced from these wells through known techniques. Operators may want to know certain characteristics of produced fluids to facilitate efficient and economic exploration and production. For example, operators may want to know flow rates of produced fluids. These produced fluids are often multiphase fluids (e.g., those having some combination of water, oil, and gas), making measurement of the flow rates more complex.
Various systems can be used to determine flow rates for multiphase fluids. In some systems, multiphase fluids are separated into their constituent phases and these phases are then individually tested to determine flow rates. Other systems include multiphase flow meters that can be used to measure flow rates of multiphase fluids without separation. These multiphase flow meters may be smaller and lighter than traditional separators and test units, and the ability to measure flow rates without separation may be desirable in some instances. Both the traditional separator systems and the multiphase flow meter systems can also be used to determine certain other fluid characteristics of interest.
It is also desirable to determine properties of the multiphase mixture, such as the presence, fraction, and salinity of water in the mixture, as this provides information about produced and/or injected water in the mixture, about the (subsea) flow-assurance measures needed to prevent hydrate formation and/or pipeline corrosion, and may affect other measurements being made on the multiphase mixture. Microwave sensors for water-conductivity detection of multiphase flows have been used with multiphase flow meters to determine water salinity, water fraction, and water-in-liquid-ratio (WLR or water-cut).
The use of electromagnetic methods, such as microwaves, has been suggested because of their high measurement sensitivity to the presence of the water phase in a multiphase flow (water permittivity/conductivity is much higher than the permittivity/conductivity of the hydrocarbon oil-gas phases). For example, U.S. Pat. No. 6,831,470, assigned to Schlumberger, shows that the fluid-contacting front-end of a microwave open-ended coaxial probe has a pressure-integrity glass-to-metal seal acting as a first pressure barrier. The back-end of the probe may have an integral N-type connector of 50-ohm characteristic impedance. The measurement probe front-aperture is mounted flush with the pipe wall of a measurement pipe section. The probe is connected through the N-type connector to the microwave electronics housed in an explosion-proof enclosure by the use of a short microwave coaxial cable/adaptor with no pressure barrier. A bulky and sometimes expensive enclosure is needed as a second pressure barrier to contain the process fluids in case the pressure-barrier formed by the probe's glass-to-metal seal fails.